In what ways is the wor vbrn8c3m0dwc271 s tih, bhm7d “work” as used in everyday language the same as that defined in physics? In what ways is it differe7mmhdn2ctrbh 0w1c s 7vbi3 8,nt? Give examples of both.

Can a centripetal forhc+s60 t-d) dscm xkakuh-w.1ce ever do work on an object? Explain.

Can the normal force on an object e5, hws2rwl:m9jb(8rkc 1quf nver do work? Explain.

A woman swimming upst(nym o6 4mxgjw96q g yia1) oq01pd5qqream is not moving with respect to the shore. Is she doing any work? If she stops swimming and me6o(qyy 0jqwg5 qnoqx9am4i1p1 6 dg m)rely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hi j/r0 ca8jj m+vbi,*jfnt: Consider what happens to the dishes when you pull a tablecloth out from ua mc,jjbf j*8+0r/ji vnder them.]

Why is it tiring to push hard aga n ;f6b-xy+5ojpj1ebainst a solid wall even though you are doing no wore pnajyxb +bfo ;15j6-k?

You have two springs that are identical excy +c/ iqa::rnwept that spring l is stiffer than spring c y+nr/w:aqi: 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on 22 k d 6zv*yxct7q66k9ju -ewa0uavbka frictionless surface (Fig.6-30). The y62kke9c 0- x vk2az6u t6uavq*7jwbd block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change when ;t2 pd;pdle7+ vife q7you jump as high as you can?qp2;df t;7ldp evie7+

In Fig. 6–31, water balloons are -ol9 1nmh fyhy1zrj-7lq -b:ytossed from the roof of a building, all with theynhyfo7-qmr:1 1lh b--9zj yl same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched fw1 g7031gmc3jlnex3u6jvao hrom a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along th16jwnmhcoul0g ev 37g3 jx1a3e trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a ykz,m3)l+94g1lii6j g h gzfhtable. If you compress the spring by pressing down 9 zfglzhgi4+1k,g3m )liy j6hwith your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wireo/ **k. g 0ekizrye+zo (Fig. 6–33). The instructor pulls the ball back and stands against theeyoz /z.g*e*oikr0k+ wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wat tj 8pxp;5 hkz/-:ljpver at the top of a waterfall fpjvx /5j:t8 ; kpl-zphalls to the pool below?

Describe the energy transformations when a child hops around on a pogo stic b)1m6rph;tv 4a e4hiuk.

Describe the energy transformations that take place whenyfa)d2ylju ymmo 45yr d*+0m+m.ux+d a skier starts skiing down a hill, but after a time is brought to rest by striking a *a+ur +md. xm yy0jdm4)d+lyuy2 m5f osnowdrift.

A child on a sled (total h-jh.-ym fn0v/ewqi 3 mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the botnf0hwhm3qe/-y i-v j.tom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather 8 uu/qfu13yefxc *;kq than stepping on top and jumping down on the other sidq f ykecqx 3*f;8u/uu1e. Explain.

Two identical arrows, one with twice the speed of the e73udd:l,du cother, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on tu3,duddc l7: ehe arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging) +c l6(;r: tead0-kgx kdqsmj pendulum in terms of energy, (a) ignoring friction, and (b) taking friction in+lqkdt k:rae ;-c)dsx06mj g( to account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greate fhmfb nt)k82/r than its original height? kf )nt8hb2/fmExplain.

Suppose you lift a suitcase from the floor to a table. Thizlo r/b1+y0(vb7 yt xe work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suryv b/+ y0(i7ztbxlo 1itcase?

Repeat Question 22 fh; .h xelp;dk1ep 4mw4or the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag tb0+ eam1ynz -twc0lbc n1zd( i5mnp46 rail than to climb straight u6ct1lpm+0-ze b41a inyd zmcb5nn 0w(p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ro) mt yor6jy,m,cs1 m+9vgu w*upes to decrease the force needed to raise a heavy load (see9mo, u6u1+ yyct),wjrmg*vms Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver falic5*teh+ , g qmg1nhv/(idy/ zls 2.80 mhm/ing+1v5 /(e ihd ct,qgz*y?    J

  A 65.0-kg firefighter 0 d* t -z-+coye6yrduzclimbs a flight of stairs 20.0 m high. How much work is required? rdozu+c*zy 6y 0-e t-d   J

  A 1300-N crate rests on the floor. How much work is requirb d 7*3w) dnylg51yxuxed to move it at constant speed (a) 4dyw )5yn* 7xgxd ul1b3.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1teec.j( jebfh ud u) mn10b6+a52tm2l 0.3 m ac.bmhu (cfu2 td j2e)0leaeb 6n5m1 +jtross a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor atk ua*g n2n5c d)wtd1ikp7 l-)z a rate of for 7.0 s. Find the net woin57u- g kz1t l)*pkd cwdna2)rk done on the box.   J

  Eight books, each 4.3 cm thick wi2j*i n3t/ 5znwh d3xguth mass 1.7 kg, lie flat on a table. How much work is required to stax 5inhj3z gd2tun 3/w*ck them one on top of another?    J

A lever such as that shown in Fig. 6-35 can.f mv:p17rjie be used to liff objects we might not otherwis.jv :rme f71pie be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kea4;b. ,; en em1on ihyw7sop*c3usnf* pt from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefmwhs *ien a7 3o1pbso*en;;cu n,y. 4fficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a 8h ob,mfh(2lk5f- brnhelicopter of mass M an acceleration of 0.10 g upwar-h 8 olf bfbrhk2,(5nmd.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distidc,3ds4at t v8r+b 0- am9abzance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as ;r,w od+ gqfo6rcyf*m0v: zo 5shown in Fig. 6–37. Determine the w*; 6o m0f,gc +fo:qdy5or rzvwork done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in t smbqegi 3w24 /ea7yg,he $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, jywni4 7g +-prwith mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speedf-2f r i,ek7nn 5agyqgut-j 04tilo53 increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electron 7sv p.p*;zrnp rnd7tp*f,ue : $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must bee 8 8*rzvhtpm/ done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averagp+:) yx vhq/sroj+8 cfe force of 110 N on the arrow over a distance of 78 cm. What isoh /v+xy)+jpr: 8scqf the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelinxzumk;j2 dcp j1r l3;2)rja/r uvo)q/wew 4a9g 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force ex jx41wrd2a ;wjl3ujpcu m; 9r/r/qav2 )zkeo)erted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what facp rhxxvlh2 5j4 s2(ps+tor will its minimum braking distaxsh2 5 2p( psj+v4rhlxnce be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inves2s)90*v: dvpx:g:trsujje s0la tv;omd;1cg tigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver )s t:x glva:d:op009js1er;*vct ;jmgvd2usslammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it ke9t3v)tdl j x:71f fkreaches the plate, it may have slowed by 10%. Neglecting gravity, estimate tk7edltjt1 v: x)39ffkhe average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-ba6 mytb bmi0,w*0ip /kg rock go if thrown straight up by someone who does 80.0 J of work on it?6wi0/byi*p 0t ,ab mmb Neglect air resistance.    m

  A 285-kg load is liftm 7f5ylt3syt3 1;2zyl z tu-wbed 22.0 m vertically with an acceleration by a single cablefu yy7s52yltt;z 1lt3 3b wmz-. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much z/:8t r, por- pabl.cemust this spring be strbppz:t8. r a-le/co ,retched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wh wz zkz52,)ydrat is the change in potential5,y2 w)zzrz kd energy?    J

  By how much does the gravitational potential energy of a 64ry n *e95fdwt/-kg pole vaulter change if his center of mass rises about 4.y*f5/td nwre9 0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speep n0*m(-g 1u4y4xj hqe.hez ,+vlzlzzd v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spelz+.lu14heg,*z (j mxynz0 zqp4-h vring?    N/m

  A 1.60-m tall person lifts a 2.16zyo;4gug6b ozo z,awp 4s, u)0-kg book from the ground so it is 2.20 m above the ground. What is the potential enerupog ;yw6)4 s,6u obgzo4zaz ,gy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top y/2jffrdj5. n ul 9e2fof a 3300-m peak.efndfl2yj9f u. 5j 2r/
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vea;gmhz cm,kh.s8 w6 w+rtically next to a ruler. The end of the spring is next to the 15-cm markm+;c mhazg ,6ws h8.wk on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and gruq;my 43 url3tabs a vine hanging vertically from a tall tree in the jungle. Hlrt4y um3q3u;ow high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides5b 0qfzhy3 lt)bw7h m+l, qi9h down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictiout9s:ys;1bed c/jp3o nless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic j jsju,t2sip4)n 0zs 4energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of pu40)j2j , ss sizjn4tmass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artis.;xsdwb.s v9 84, awf mtaytt6t jumps vertically upward from the top of a platform with a svt9.tfmw;.d4a t6sb8y xw,a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constant is *;v zt: 1 ..z)hgv gpfe2gbxai950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed caag1*pef.i zgh t g.z;vxbv2) :n it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction al+ q wbxxlne5n* z5s0b9ong the looped track shown in Fig. 6–39. If 5eqwz+9b0nn5s bxx*l the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the .nj k 4ghj3of-:yl-nuij+d ,v end of a spring (spring stiffness constant k), Fig. 6–40.y do-n+if:3,jj nk -v jlh4ug. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She 4/g5 3t oy2lgr 8jpy.xatpzh5is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constgah 4r /gypz5o35yx8ltj .2tp ant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car smwnez:pg6u/ 2l xebx )ks*6ue 4ly /+chown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at po: bg/y+l xl*emn6u4uzxecwe/2 k p) 6sints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a p b /.0vivy/ma h /9robyz/ etz804kayspeed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bot:wc cb;(+;vl ip p3 p4bdl/0woj.m geftom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that 0o f: vwe ;m4+lcbj ; b/.iwp(gpc3dlppassengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8s3axq 7tr/t +mpw5s t8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95j:il3-mcms +wnc kjq 4:fvs 3,km/h in opposite directions, collide head-on and com sc3qml j:fvj ic+wn4s-:k 3,me to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slidq(;o9f;lzuov0 n5 hxme 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction wluv9zoo5m; qhx(f; n0as generated in this process?    J

  A ski starts from rest and slidescn.6kj;ed(5h iekmz ( down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the ground.bqf q5y.)0px(bxr/sl m2y v)+vycwj6
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a hei+d2ij hnn5q y;ght of 2.0 m, and it bounces back to a height of 1.5 m. +j; yn2qnd5 ih
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is -f zs1qh; l d6,fwr5*big1 lb5k-ifewpulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficw b-h;w1i6rf l5f1l-,eq i*fdb ks5 gzient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a sp*ryqt4spt2kol3*w* w eed of If the average force of friction is equal to one-fifth of its weight, with what speed will it2 t sw*krw oq3y4**plt reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches t7i-md;l.- sqdqw, k aihe foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is fi3p9yr uo9cjlxx )0r-zrmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic ur cjxzx3 o9) r9y-l0pfriction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizo9-hr9n a lmv*st g+ga0ntal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swil tn9amsg9hrgv 0-a+*ng?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 v qe0(e 3.v90lhbb 6d;zmatmz kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed ofvhbe0bv 03 qz96.mad;m( tzel 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-ctl:di *a6ou*l/ ox1gstory wind*ld o1x/6uit:l *o gcaow 16.0 m above?    s

  If a car generates 18 hp when traveling at1a euj+wq 9 kcr4fe1+q a steady 88km/h what must be the average force exerted on the car due to fricc+ajrqueq91 4 f+wke1tion and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is t.s(6id q+ .ftcewnt,o: z 5gvfhe average power delivered by,v owt:tdifzsce+. .f(qn6g5 the engine?$\approx$    hp

  (a) Show that one British horyf eo ,,tz1+9 ygirjp8sepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are ofte1fhnna.t 3w/g s(k81e)rv tupn expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg carbwff-t-v ea; 66 f-p8ogc,uz f slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the cef-z v,f8atcw -- ; 6fopugfb6ar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do t w7lu u0iorwf/ s,0a;in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fa0 5lgr:xv5(e /gc uqfrom rest to 14m/s If this motion takes 1.5 s, whl5 f/c (ugex 0rvga5:qat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a h3(0fs; c wfh zuc2wz:9 jz:nmneight of 3.60 m. What output rating (watts) should the pump motof uw:cn3fs z0wjzcznmh;:2 (9 r have?    W

  During a workout, the football players at State U. ran up the stadiup gjctfmxz0o* / v95)pm stairs in 66 s. The stairs are 140 m long and inclined at an angg5v)txm9j f z/0*oc pple of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist clg) 8k*fymqt h-drms6tptpr369 ( gq 4pimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power vhbh b70b)pzd41ht, l output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h i zhhbdh l,14bv7 b)p0tf the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310lw/,xmf; 3jvc -kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.cfv,; xjl/w 3m45?    hp

  A bicyclist coasts down a 7. ;ncp1h qf;1po0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s c u4pmn:a9 pqv5ebe, k)ars have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compre:p,uapbe )k4nqv em95ssion of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off thjcpf-n,t5c sh *srx2, e ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work i5*,rccn2sph sxt ,j-fs required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics shows -4ienczkqd, - 9r kuz7that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the ak-qrz 94u ein kd7,-czrc?   m/s

  The block of mass m sliding without friction along the looped track shown in x6 dbc3fk 1.zxFig. 6–39 is to remain on the track at all times, even at thezxb6 k xdf.3c1 very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hix* xuuf+of)6 ms parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal v +x*uuffmo x6)elocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal coofz8rim*4a )fyo+ pj3g y:*k yrd of length L whose other end is fixed (Fig. 6–43). foy *y48f g pzkmy)oa:3+*j ir
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 37 r69vis2qg xr4j*u5fi00-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 45vr69jriquf 2*xgs im. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28f6c*ly jznui m,i69w8 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts cz*d+khrbry9*da ; d o9an move 47,000 people per hour. If the average lift carries people about 200 m (vertically) highe*bd9r+o d9z;hd *yrakr, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m 8mi1 3s.jh7t2 vz8zt4 ;g13 dmhnhgpcxee1as before striking the turbine blades s2h1vp .z nexj1 dctg1m3;38i47tgmh8aze hs. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), the -2 s5q oqfe+bpdifference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your b +op25f- eqqsweight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, ibrsf7 9pcxd9wxd: -8 how high could an 82-kg man climb a ladder ifs -b9c8dwp 9r: dxxf7i he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at ani x 1a8csv,vc4md/f 4ugjp z69 upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside t c/b(qo -e1iyche scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does th/eq ci -(coyb1e scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, 9 /y5ggdg pyd/and swings out over a lake (Fig. 6–45). He releases thedy/gg/ y 5pd9g rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a v.rr(jypuvn ilqh. c89q+a.b/ ertical distance of 5.0 m in 9.0 s. What minimum power output was used v/+nb.cqrpjrlhy.9 8q a(i.uto accomplish this feat?    W

  Some electric-power companies use water to store en rks;f,zynvy0d, *cr0vekkj yl.899 bergy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the ene.,fynj by z0dk 9,rk9y0e*vv k8; rsclrgy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness conm/em q *m oi8n0xqz1ko.:w,ed stant k is cut in half. What is the spring stix/d*0m1we:qk eq,izom.n8 m offness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed )xi,7wc0+ d shlfdw z68.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55kj o3k ;urfh4u4pis8k2 z:4g umm/h in 3.2 s, how long will it take to accelerate from 55p3 jufo842k4 uu hgisr 4z:;mkkm/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (theqc;px78 ap:rp “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmip8q7p;x:ap r cll is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upqglmeo )j1 p:y77 (tjzward a distance of 500 m, what was 1)ej 7lmypj(oz qtg7: its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at q m2 ;urmrh f(+j/ *tj5.hcajqa rate of 95kg/s (a) If this water whee jj5fmm;hu .qacjhq+t(2/r *rl is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s